The present invention relates to a connection of such a cable as a wiring harness to electric devices or the like in a motor vehicle or the like. More particularly, the invention relates to a connection structure of a shielding connector for relay connecting a shielded cable to a printed circuit board in the electric device and an antenna.
An electric device in a motor vehicle, such as a car navigation system, contains a control-use printed circuit (PC) board on which electronic parts, IC (integrated circuit) packages and others are mounted. Recently, a transmission speed of an electric signal transmitted to and from the PC board is increased (viz., the transmission signal frequency is increased). Further, board patterns of the PC board are densely arranged. To transmit such high frequency signals, a shielded cable designed to be adapted for the high frequency signal transmission is generally used. With increase of the transmission signal frequency, also in the shielding connector for relay connecting the shielded cables, there is an increasing demand to take some measure for the high frequency signal transmission.
A called coaxial cable is known as an example of the shielded cable. Usually, the shielded cable has a coaxial structure having a signal conductor which is formed by binding a plurality of element wires and serves as a signal transmission line, a shielding conductor consisting of a plurality of braided element wires, an insulating member interposed between the signal conductor and the shielding conductor, and a sheath covering the outer periphery surface of the shielding conductor. The shielding conductor closely covers the outer periphery of the insulating member to thereby electrically shield the signal conductor.
Generally, the shielding connector for relay connecting coaxial cables for transmitting high frequency signals is formed with an internal conductor terminal to be connected to the signal conductor for transmitting a high frequency signal, an outer conductor terminal which is to be connected to the shielding conductor of the braid wire or the like and covers the internal conductor terminal for the electromagnetic shielding purpose, and a dielectric body of a predetermined dielectric constant provided between the internal conductor terminal and the outer conductor terminal. The shielding connector individually and electrically relay connects the signal conductor and the shielding conductor of a shielded cable to be relay connected, which are exposed by peeling the connection terminal and the insulating member off the shielded cable.
A typical example of such a shielding connector is disclosed in the Unexamined Japanese Patent Publication No. 2000-173725. FIG. 4A is a longitudinal sectional view showing the shielding connector, and FIG. 4B is a cross sectional view taken on line Bxe2x80x94B in FIG. 4A. As shown, an insulating member and a sheath 71c of a coaxial cable 71 are peeled off to expose a signal conductor 71a and a shielding conductor 71b. A connection process of connecting the shielding connector to the coaxial cable follows. To start, a press connection part 72a of an inner conductor terminal 72 is press connected to the exposed signal conductor 71a. Then, the inner conductor terminal 72 is forcibly inserted into and fixed to a press-fitting bore 74a of a dielectric body 74, which has been put in and assembled to an outer conductor terminal 73. The shielding conductor 71b as is inverted on the coaxial cable 71 is put on a press connection part 73a of the outer conductor terminal 73, and compressed by the latter. Then, the sheath 71c and the shielding conductor 71b are both clamped with the press connection part 73a of the outer conductor terminal 73. Here, the connection work is completed.
In the step in which the inner conductor terminal 72 is forcibly inserted into and fixed to the dielectric body 74, which the step is executed before the step of clamping the shielding conductor with the press connection part 73a of the outer conductor terminal 73, a terminal insertion hole 73b, which is formed by opening the upper surface of the outer conductor terminal 73 to an upper part of the drawing, is utilized as a press-fitting work space, whereby the inner conductor terminal 72 may easily be press inserted into the connector by means of a press-fitting jig or another tool.
Another conventional art is disclosed in the Unexamined Japanese Utility Model Application Publication No. Hei 3-80982. FIG. 5A is a longitudinal sectional view showing the shielding connector and FIG. 5B is a cross sectional view taken on line Cxe2x80x94C in FIG. 5A. As shown, an insulating member and a sheath 81c are peeled off a coaxial cable 81 to expose a signal conductor 81a and a shielding conductor 81b. In a step of connecting the shielding connector to those exposed parts, a dielectric body 84 and an inner conductor terminal 82 are assembled to an outer conductor terminal 83 in advance. The signal conductor 81a and the shielding conductor 81b are respectively put on a press connection part 82a of the inner conductor terminal 82 and a press connection terminal 83a of the outer conductor terminal 83 to which those conductors are to be connected. The former conductors and the latter terminals are press connected together simultaneously by using a press connection jig D or another appropriate jig. Then, the connection work is completed. For the press connection work of connecting the press connection part 82a of the inner conductor terminal 82, a press-inserting hole 83b is opened to an upper part and a lower part in the vicinity of the press connection part 82a of the outer conductor terminal 83. With the press-inserting hole, the press connection part, together with the coaxial cable 81, is press connected simultaneously to thereby providing easy connection.
Generally, the characteristic impedance of the transmission line for the high frequency signal transmission is set at 50 xcexa9, for example. The high frequency signal transmission line is impedance matched to the signal transmission paths of the PC board of the electric device to be relay connected or the cable also to be relay connected. If the transmission path contains a part where the characteristic impedance is not matched (impedance mismatching part), the signal reflects at the impedance mismatching part to reduce the transmission efficiency, and noise is generated thereat. Accordingly, the shielding connector as a relay connection part in the transmission path is also impedance matched to the signal transmission line.
The impedance of the shielding connector is matched to that of the shielded cable as the transmission line by adjusting a xe2x80x9cratio of the inside diameter of the body of the outer conductor terminal and the outside diameter of the terminal part of the inner conductor terminalxe2x80x9d and xe2x80x9ca dielectric constant of the dielectric bodyxe2x80x9d. As shown in FIGS. 4 and 5, the diameter of the press connection part 72a (82a) after the inner conductor terminal is press connected is designed to have a size and a shape, while giving priority to a reliability of its electrical connection to the signal conductor. Usually, it is smaller than the diameter of the terminal body. It does not satisfy the xe2x80x9cratio of the inside diameter of the body of the outer conductor terminal and the outside diameter of the terminal part of the inner conductor terminalxe2x80x9d. Further, a part of the wall of the outer conductor terminal near the press connection part is opened to secure a space for the work using the press-fitting jig or press-inserting jig. The press connection part as the connection part to the signal conductor of the inner conductor terminal is not covered in all directions with the outer conductor terminal provided for the electromagnetically shielding purpose and the dielectric body, and is exposed to air having a dielectric constant of xcex5r=1. For this reason, the impedance of this part is not matched to that of the transmission line, and is higher than that of the shielded cable.
The transmitted electrical signal is reflected or radiated at the part where the impedance of the shielding connector is not equal to that of the shielded cable, and in this case, a normal transmission of the signal is impossible or noise is generated. Those disadvantageous phenomena are remarkable particularly in a frequency region of several GHz of the transmitted signal.
To cope with this, what a designer has to do is to lower the impedance at the press connection part of the inner conductor terminal so as to be matched to the impedance of other parts of the shielded cable and the shielding connector. Therefore, the impedance matching may be achieved by selecting the diameter of the press connection part of the inner conductor terminal after its press connection to be nearly equal to that of the body of the outer conductor terminal. A conventional method to increase the diameter of the press connection part is to wind a metal tape around the press connection part, and another method is to further press a cylindrical metal sleeve from its outside to increase its diameter.
The method of winding the metal tape has the following disadvantages. The manual work is essential to the work of winding the metal tape. In the case of the small connector, the metal tape must be wound on an extremely thin press connection part of a small inner conductor terminal. This work is extremely delicate, and it is almost impossible to impart a satisfactory working accuracy to such a press connection part. Further, if the tape turns aside, it will come in contact with the outer conductor terminal and cause a shortcircuiting problem. Additionally, it is very difficult to achieve an attempt to reduce the time taken for the step (terminal processing) of connecting of the connector and the cable to thereby reduce the cost to manufacture.
The method of further pressing a cylindrical metal sleeve from its outside to increase its diameter has the following advantages and disadvantages. This method enables the press connection process to be automated mechanically. In this case, the automated press connection is performed at the time of the cable terminal processing when the cable is connected to the connector. Accordingly, a sleeve pressing machine must be installed additionally every terminal processing line in an automated cable terminal processing factory. This results in increase of cost. Further, in some type of cable, the thickness of the signal conductor per se is varied, and a shape of the press connection part of the inner conductor terminal to be press connected to it is varied. Accordingly, the cross section size of the press connection part of the inner conductor terminal is also varied, and the outline of the sleeve to be pressed is varied. As a result, it is difficult to impedance match it to various types of cables.
Accordingly, an object of the present invention is to provided a shielding connector which ensures an impedance matching in the connector to thereby reduce the signal transmission loss by signal reflection and the like, and provides an easy terminal processing to the cable terminal.
According to the present invention, there is provided a shielding connector in which an inner conductor terminal to be connected to a signal conductor of a shielded cable is put in a cylindrical outer conductor terminal containing a dielectric body, and a shielding conductor of the shielded cable is connected to the outer conductor terminal, the shielded cable including the signal conductor, the shielding conductor, and an insulating member interposed between the signal conductor and the shielding conductor, and the shielded cable being covered with a sheath. In the shielding connector, a terminal insertion hole is formed in the outer conductor terminal in order to put the inner conductor terminal in the outer conductor terminal in connection with the dielectric body. The inner conductor terminal is put in the outer conductor terminal in a state that a connection part at which the inner conductor terminal is connected to the signal conductor is exposed within the terminal insertion hole. A conductive small diameter member which electrically reduces a diameter of the terminal insertion hole in the vicinity of the exposed connection part toward the connection part is provided in contact with the inner wall of the outer conductor terminal.
In the shielding connector thus constructed, the diameter of the connection part of the inner conductor terminal is increased in conformity with the outer conductor terminal. The diameter of the outer conductor terminal at that part is reduced in conformity with the connection part. The conductive small diameter member which electrically reduces a diameter of the terminal insertion hole in the vicinity of the exposed connection part toward the connection part is provided in contact with the inner wall of the outer conductor terminal.
With such a construction, the outer conductor terminal after its connection to the signal conductor of the shielded cable may be put in the dielectric body which is previously put in the outer conductor terminal by utilizing the terminal insertion hole formed opening a part of the wall surface of the outer conductor terminal, as in the conventional shielding connector. Further, the impedance in the vicinity of the press connection part at which the inner conductor terminal is connected to the signal conductor which, in the conventional technique, is high since the press connection part is exposed outside through the opening of the outer conductor terminal, is successfully reduced by electrically reducing the diameter of the opening of the outer conductor terminal at the corresponding part by using the small diameter member.
Accordingly, this part in the connector is impedance matched to another portion. In this respect, the impedance mismatching problem is solved. Accordingly, the signal reflection at and radiation from that part are reduced, and the resultant connector handles transmission signals of higher frequencies. Further, use of the small diameter member reduces the opening area of the terminal insertion hole. This feature reduces the radiation noise and incident noise quantities. In this respect, the resultant shielding connector has excellent characteristics.
For the terminal processing of connecting the connector to the terminal of the shielded cable, the small diameter member is merely provided in contact with the outer conductor terminal, while in the conventional connector needs the process of manually increasing the diameter of the press connection part by using the metal tape, or the process of pressing the metal sleeve. Therefore, the processing accuracy is good, and the terminal processing is easy.
When the small diameter member is installed to the dielectric body, the connector terminal processing cost is reduced. When the dielectric body and the small diameter member are one-piece molded, the connector terminal processing cost is reduced, and a number of required parts is reduced.
When the small diameter member is press fitted into aid outer conductor terminal, the connector is free from the impedance variation caused when the connector is vibrated by external force and the inner wall of the outer conductor terminal comes in contact with the small diameter member. Accordingly, good contact performance is ensured, and stable performances are then secured. When the small diameter member is resiliently put in the outer conductor terminal, there is no chance that the connector is vibrated by external force and the inner wall of the outer conductor terminal comes in contact with the small diameter member, and the impedance is varied.